The ultrasonic flow rate measuring device is a device that measures a propagation time of an ultrasonic wave which is caused to propagate across a measurement passage while flowing a fluid through the measurement passage, and detects a flow rate of the fluid based on the measured information.
An ultrasonic wave transmitter and an ultrasonic wave receiver are provided respectively to the opposing short sides of the measurement passage, whose cross-section is rectangular.
The ultrasonic wave transmitter and the ultrasonic wave receiver face each other and transmit/receive an ultrasonic wave between them along a line, which intersects with the flow direction of the measurement passage at a predetermined angle.
Also, an ultrasonic flow rate measuring device has been proposed in which the measurement passage is constructed of multi-layered passages formed by partitioning the measurement passage with a plurality of parallelly arranged partitioning plates in order to improve the measurement accuracy.
Yet, another ultrasonic flow rate measuring device has been proposed in which a plurality of ultrasonic flow rate sensors (a first ultrasonic wave transmitter-receiver and a second ultrasonic wave transmitter-receiver) are arranged in the measurement passage to acquire a plurality of flow rate measurements, an average of which is calculated to determine a conclusive flow rate measurement (Patent Literature 1).
In Patent Literature 1, respective ultrasonic flow rate sensors are arranged to create ultrasonic wave propagation paths at different angles.    Patent Literature 1: JP-A-2002-257607